1. Field of the Invention
This invention relates to power transmission belts and, more particularly, to a power transmission belt having a bias cut side surface. The invention is further directed to an apparatus for forming a power transmission belt/belt sleeve, including those having a bias cut side surface.
2. Background Art
It is common to manufacture V-belts by initially forming a belt sleeve consisting of rubber and other component parts. The belt sleeve is vulcanized and thereafter cut to produce individual belts having a trapezoidal cross-sectional shape. This conventional manufacturing process often results in structural variations that may compromise the performance of the belt and its operation. The length and cross-sectional shape of the belt may vary due to thermal shrinkage of material defining the belt. Load carrying cords, between tension and compression sections, may be less than optimally located. Other flaws may occur in the machining process that result in the production of a belt with less than the desired quality.
Of these problems, the variation in cross-sectional size and shape is of particular concern. This condition may cause the position of a belt within a cooperating pulley groove to fluctuate in a radial direction relative to the pulley axis. This fluctuation may cause vibrations to be induced during running. This condition may also cause fluctuation in the belt tension, which may cause vibration of pulleys, around which the belt is trained, and associated machinery.
To address the above problem, it is known to subject the individual V-belts, cut from a sleeve, to a sanding process. An exemplary structure and method for accomplishing this are shown in the Official Gazette of Japanese Patent No. 3553371. The cut belt is trained around a pair of pulleys and driven in an endless travel path. As the belt is traveling, the sides are polished to be brought within dimensional tolerances.
One advantage associated with polishing the side surfaces is that a substantial area of short staple reinforcing fibers becomes exposed at the belt side surfaces. As a result, the coefficient of friction between the side surfaces and cooperating pulleys is decreased, as a result of which noise generation, particularly at startup, is maintained generally at an acceptably low level. On the other hand, as the belt slips, due to the reduced coefficient of friction, unwanted abrasion and heat generation may occur.
In an alternative process, the vulcanized sleeve can be turned inside out and placed on a mandrel. While rotating the mandrel, V-shaped grooves can be cut into the sleeve using a grinding stone, after which a cutter is employed to separate the individual belts. An exemplary structure and method of forming belts in this manner are described in U.S. Pat. No. 3,818,576.
A further apparatus and method for forming V-belts are shown in the Official Gazette of JP-B-4-2425. An apparatus is disclosed therein including a driving pulley and a driven pulley around which a belt preform is trained for movement in an endless path. The driven pulley is movable along a guide rod. A pair of rotatable cutting blades are used to reconfigure/form the belt sides. A pushing roller is provided at a cutting location to bear against a back face of the belt to reinforce the same as the cutting blades are pressed against the belt. The cutting occurs as the belt is driven and the cutting blades rotate.
With this apparatus, the rotary cutting blades are arranged relative to each other such that both sides of the belt are interposed between the rotary cutting blades to be simultaneously operated upon. As a result, relatively large components may be required for the cutter, including the cutting blades, to effect the required cooperative movement between the belt and the cutter. Generally, with increased complication and size of an apparatus, weight and manufacturing expense correspondingly increase.
In Official Gazette of JP-A-55-28883, an apparatus and method are shown wherein cutting of a belt sleeve is carried out so that the finished forms of adjacent belts coincide at their sides. As a result, the amount of material that is removed and must be disposed of, or otherwise handled, is reduced compared to a system wherein there is a spacing between adjacent belts.
With the sides of adjacent belts coincident, a certain amount of material can be saved. However, there is still a significant amount of scrap that results. Thus, there is still room for improvement with respect to minimizing scrap generation.
This latter method is preferable in this regard to the previously described methods, which generate considerable scrap or waste material. For example, the cutting blades may remove a significant, ring-shaped scrap at each side surface. Scrap generated through grinding, shaving or polishing may likewise be significant in the above-described methods. Generally, there is a strong desire to reduce the quantity of scrap generated during the belt forming process both to save material and time as well as avoid inconvenience associated with handling the generated scrap.
It is also an objective of designers of this type of equipment to provide structure that is compact and affordable, yet capable of producing high quality power transmission belts. Another aim of designers of such systems is to allow these processes to be carried out in a time efficient manner.